<meta charset="UTF-8">
<form class="form-inline ml-3">
  <div class="input-group input-group-sm">
    <input class="form-control form-control-navbar" type="search" placeholder="输入单证号" aria-label="Search">
    <div class="input-group-append">
      <button class="btn btn-navbar" type="submit">
        <i class="fas fa-search"></i>
      </button>
    </div>
  </div>
</form>